The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, an exhaust gas recirculation system is installed in most diesel engines and some gasoline engines which are installed in a vehicle to cope with regulations of exhaust gas.
The exhaust gas recirculation system returns some of exhaust gas discharged from the engine to an intake device of a cylinder to lower a combustion temperature of the engine to reduce a generation amount of nitrogen oxide (NOx), and reduce fuel consumption.
A low-pressure EGR apparatus adopts a scheme in which exhaust gas formed at a rear end of a particulate filter is cooled with an EGR cooler and is recirculated. Accordingly, since the low-pressure EGR apparatus is longer and lower in pressure than the existing high-pressure EGR apparatus and longer in flow path of the EGR gas, the low-pressure EGR apparatus cannot be stable in terms of responsiveness and controllability.
In addition, in an engine using a low pressure exhaust gas recirculation (LP EGR) technology, while the recirculated exhaust gas is used at a set ratio (e.g., 10 to 20%) with respect to air intake, when a vehicle is switched to a coasting drive mode according to an operation state, a throttle valve is closed and the recirculated exhaust gas remains between the throttle valve and an EGR valve.
We have discovered that combustion stability may deteriorate by the recirculated exhaust gas which remains in the coasting drive mode (accelerator pedal tip out) and engine hesitation can occur due to unstable combustion of the engine in reacceleration.